1. Field of the Invention
The present invention relates to a method of producing an aromatic carbonate from an aromatic hydroxy compound, carbon monoxide and oxygen using a specified catalyst system. An aromatic carbonate, particularly diphenyl carbonate is useful as a raw material for polycarbonate or the like.
2. Description of the Related Art
A method of reacting an aromatic hydroxy compound with phosgene is generally used for producing an aromatic carbonate. However, this method has many problems as an industrial production method because of the high toxicity of phosgene and the by-production of large amounts of inorganic salts.
Some methods have thus been proposed which do not use phosgene in which an aromatic carbonate is produced from an aromatic hydroxy compound, carbon monoxide and oxygen.
Japanese Patent Publication No. 56-38144 discloses a method which uses as a catalyst a palladium compound, a compound containing a metal from the groups IIIA, IVA, VA, VIA, IB, IIB, VIB or VIIB in the periodic table, and a base. Japanese Patent Publication No. 56-38145 discloses a method which uses a palladium compound, a manganese or cobalt complex, a base and a desiccating agent. Japanese Patent Laid-Open No. 1-165551 discloses a method which uses a palladium compound, iodine and zeolite. Japanese Patent Laid-Open No. 2-104564 discloses a method which uses a palladium compound, a bivalent or trivalent manganese compound, tetraalkylammonium halide and quinone. Japanese Patent Laid-Open No. 2-142754 discloses a palladium compound, a bivalent or trivalent cobalt compound, tetraalkylammonium halide and quinone. Japanese Patent Laid-Open No. 5-25095 discloses a method which uses a palladium compound, a cobalt compound, an organic or inorganic halide and a basic compound.
Japanese Patent Laid-Open No. 5-58961 discloses a method which uses a palladium compound, a cobalt compound and an alkali metal halide.
Japanese Patent Laid-Open No. 5-97775 (U.S. Pat. No. 5,142,086 and European Patent Laid-Open No. 507,546-A2) discloses a method which uses a catalyst system comprising (a) a palladium compound; (b) a quaternary ammonium salt; (c) an inorganic compound as a cocatalyst selected from cobalt, iron, cerium, manganese, molybdenum, samarium, vanadium chromium and copper compounds; (d) an organic cocatalyst selected from aromatic ketones, aliphatic ketones, and aromatic polycyclic coal tar hydrocarbons.
However, thee methods have critical problems concerning the low activity of the catalyst used, and the low yield of an aromatic carbonate based on the starting aromatic hydroxy compound, and re thus unsatisfactory as industrial production methods. Tis is supposedly due to the phenomena where the activity of the catalyst used is decreased by the water produced by reaction, and that hydrolysis o an aromatic carbonate is accelerated in the conventional catalyst system. The methods proposed for preventing this phenomena include a method of using a large amount of coexisting dehydrating agent or removing the water produced (Japanese Patent Laid-Open No. 54-135744) and a method of distilling off the produced water by reaction distillation (Japanese Patent Laid-Open No. 4-261142). However, it could not be said that these methods have sufficient effects.
The conventional methods also have the problem that large amounts of by-products, particularly phenoxyphenols which cannot be easily separated from an intended product, are produced by oxidation of an aromatic hydroxy compound.